全文获取类型
收费全文 | 355905篇 |
免费 | 2392篇 |
国内免费 | 638篇 |
专业分类
化学 | 170215篇 |
晶体学 | 5410篇 |
力学 | 18521篇 |
综合类 | 9篇 |
数学 | 52549篇 |
物理学 | 112231篇 |
出版年
2019年 | 2293篇 |
2018年 | 11089篇 |
2017年 | 11870篇 |
2016年 | 8215篇 |
2015年 | 3410篇 |
2014年 | 4387篇 |
2013年 | 10777篇 |
2012年 | 12033篇 |
2011年 | 21169篇 |
2010年 | 13568篇 |
2009年 | 13463篇 |
2008年 | 18861篇 |
2007年 | 22219篇 |
2006年 | 9055篇 |
2005年 | 13927篇 |
2004年 | 10451篇 |
2003年 | 9879篇 |
2002年 | 7944篇 |
2001年 | 7474篇 |
2000年 | 5964篇 |
1999年 | 4396篇 |
1998年 | 3898篇 |
1997年 | 3861篇 |
1996年 | 3754篇 |
1995年 | 3434篇 |
1994年 | 3580篇 |
1993年 | 3265篇 |
1992年 | 3731篇 |
1991年 | 3735篇 |
1990年 | 3672篇 |
1989年 | 3540篇 |
1988年 | 3654篇 |
1987年 | 3543篇 |
1986年 | 3359篇 |
1985年 | 4444篇 |
1984年 | 4730篇 |
1983年 | 3959篇 |
1982年 | 4091篇 |
1981年 | 4017篇 |
1980年 | 3990篇 |
1979年 | 3975篇 |
1978年 | 4293篇 |
1977年 | 4140篇 |
1976年 | 4229篇 |
1975年 | 3897篇 |
1974年 | 3938篇 |
1973年 | 4127篇 |
1972年 | 2883篇 |
1971年 | 2399篇 |
1970年 | 2205篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
E. V. Zakharov A. G. Davydov Yu. V. Pimenov G. M. Tikhonov 《Computational Mathematics and Modeling》1991,2(1):79-84
Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 119–127. 相似文献
222.
We consider a resource management problem in which the management objective is to minimize fluctuations in resource stocks. Stabilizing management policies constitute the designing of memoryless state feedback control strategies for a discrete time resource model which contains unknown but bounded fluctuations. We also show that the problem of maximizing sustainable yield in an uncertain fishery can be considered as the problem of stabilizing of the stock level.The paper corresponds to an invited talk at the 14th Symposium on Operations Research, Ulm, September 6–8, 1989.The support by Yrjö Jahnsson Foundation is gratefully acknowledged.This work was supported by NSF and AFOSR under grant ECS 8602524. 相似文献
223.
The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate
only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the
carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in
the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are
obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities).
Variation of FCA is numerically studied with photon frequency and well width. 相似文献
224.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献
225.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
226.
The direct regioselective C–H arylation of 3-methoxythiophene and 3,4-ethylenedioxythiophene (EDOT) was performed successfully under ‘Heck-type’ experimental conditions. This novel synthetic methodology has been used to prepare in a more simple way a series of oligothiophenes interesting for the electronic industry to build new synthetic organic materials. 相似文献
227.
The synthesis of rigid spirocyclic bislactams derived from pyroglutamic acid has been established. 相似文献
228.
V. G. Osmolovskii 《Journal of Mathematical Sciences》2006,135(6):3437-3456
All the equilibrium states of a one-dimensional variational phase-transition problem are explicitly found. The temperature-dependence
of the stability of one-phase equilibrium states is studied. Bibliography: 5 titles.
__________
Translated from Problemy Matematicheskogo Analiza, No. 32, 2006, pp. 3–19. 相似文献
229.
230.